A number of mutually different arrangements are known to the art, by means of which particles can be transported with the aid of quantities of air placed under an overpressure.
Such transportation normally requires the use of large quantities of air per quantity of particles transported. Such air to particle weight ratios have been found to provide reliable particle transportation, with but small risk of stoppages occurring in the transport conduit system. It is also known that because the main bulk of the medium transported in such cases is air, large quantities of energy are required per weight quantity of particles in order to transport the particles effectively. The wear on the conduits and valves incorporated in such transportation systems is also extremely heavy, due to the high speeds at which the particles move and the high-velocity impact of particles striking against the conduit and valve walls.
When the particle quantity is increased, however, so that the weight ratio of particles to air in the transport conduit system is greater than one, the transported medium is said to be transported in a "dense-phase"-relationship. When the particles are present in higher weight percentages, the particles, or powder, stream through the conduit system in the manner of a liquid. Friction between the individual particles is reduced by air which flows therebetween. If the weight percentage of particles was to be increased still further, insufficient air would be present to allow the particles to move relative to one another. The particles would then be transported in the form of a "solid mass", which is pushed in front of the pressurized air applied.
Much less energy is required to transport particles in a dense-phase-relationship than in a relationship in which the weight quantity of particles per kilogram air is lower, and also results in less wear on the conduits, since particle speeds, in this case, are extremely low, for example 3-5 m/s.
It is well known in this art that an increase in the weight percentage of particles present results in a pulsating flow of material. This is particularly true in those cases where the particles are transported over longer distances, since in this case the particles collect to form "waves", which travel intermittently along the conduit, reaching the discharge end thereof in a discontinuous flow.
It is also known that an increase in the particle/air ratio will increase the risk of stoppages in the transport conduit system.
It is further known that when particles are transported in a dense-phase relationship it is necessary to place under pressure a container, a so-called dispatching vessel, which is filled either totally or partially with the particles to be transported. Consequently, the transportation of particles is normally discontinuous. When the container was been emptied of particles, the transportation of particles is interrupted and the conduit system blown clean, whereafter the dispatching vessel is again filled with particles and re-pressurized.
In order to overcome this discontinuity in particle flow, however, and to render the process continuous, it is known to provide two particle dispatching vessels which operate alternately, to dispatch particles to one and the same particle transport conduit, or to gate particulate material into a dispatching vessel constantly held under pressure.
All known particle transporting systems which operate with high particle/air mixtures, however, deliver the material intermittently, i.e. in time varying flow distribution.
Neither is the particle velocity and particle outflow controlled in hitherto known constructions. The magnitude of the required overpressure is contingent on the length of the transportation path, and consequently the conditions at the outlet end of the conduit system are also determined. The transport system delivers particulate material at a given maximum capacity, but without affording the possibility of regulating the flow and its distribution in time.
A method for transporting disintegrated solid particles in a "dense-phase"-relationship is described and illustrated in the U.S. Pat. No. 4,191,500, this method comprising the steps of
(a) filling a supply container with disintegrated particles; PA1 (b) sealing the container; PA1 (c) supplying a vehicle gas to the sealed container through an inlet which is placed under pressure to an extent such as to create a momentary pressure level which exceeds the level of pressure in a downstream located supply conduit; PA1 (d) opening a valve, which connects a lower part of the container to said downstream supply line, such as to effect particle feed in response to the pressure difference thus created and to the expansion of gas in the particle interstices; and PA1 (e) supplying further gas through said pressurized inlet, through said container to an extent sufficient to both maintain the pressure difference between the container and supply conduit and to cause the particles to move from the container through said valve and supply conduit to an outlet.
To the prior art relevant to this technical field belongs the France patent specification No. 2,159,182 in which is described a construction where solid particles passing into a container in varying concentrations and where said particles are leaving said container in a lower end having a less varying particle concentration.